The quality of service requirements for different types of information carried by a network are often themselves different. For example, it can be more important to limit the latency (the delay between the time a signal is sent and the time it is received) and the error rate for voice information (e.g., conversations) carried by a network than for a file transfer carried by the same network. Even short delays in voice conversations lead to confusion because they can cause one party to mistakenly believe that the other party is finished speaking. This can cause one party to talk over the words of another party. Short delays in file transfers are typically not noticed. Likewise, a high error rate in voice conversations can render a party's words incomprehensible. A high error rate in file transfers is typically handled without too much inconvenience using known error detection and correction protocols, and retransmissions.
A network typically has a finite capacity to carry information at a given quality of service. Thus, meeting stringent quality of service requirements for one type of information can mean limiting the amount of other information carried by the network, or reducing the quality of service with which the other information is carried. One known scheme for carrying this out is the H.323 standard. The H.323 standard specifies gateways interposed between end-user terminals on a network. The gateways act as “traffic cops,” monitoring the state of the network and quality of service requirements, and deciding what information an end-user terminal can send and receive, and by what parameters (e.g., rate, protocol, etc.) An H.323 gateway negotiates with another H.323 gateway to determine the parameters for a communication between end-user terminals represented by each gateway. This communication is typically performed on a link-by-link basis (e.g., it is performed for each new communication between two or more end-users), and disadvantageously generates network traffic that can additionally burden a network. Further, a H.323 gateway's end-user terminals have no real control over the parameters of a communication, as these are dictated by the gateway.
Another known system involves direct negotiations between endpoints to determine the parameters of a communication. Again, this is performed on a link-by-link basis, and can generate substantial amounts of network traffic when performed on a large scale (between many endpoints at once).
Yet another known system employs a gateway that monitors the status of the network and then acts as a filter between the gateway's end-user terminals and the network, deciding what to pass on to the network and what to defer or drop, based upon the network's status (e.g., based upon the level of congestion of the network). The use of a gateway is expensive and adds an additional layer of complexity to network topology.
A better system would assure quality of service for a particular type of information carried by a network without generating the substantial overhead traffic involved in two-way negotiations over communications parameters on a link-by-link basis, and avoid the expense and added complexity incurred by using gateways between the network and the end-user terminals.